The chip I photographed is the i486 SX, which is the...

The chip I photographed is the i486 SX, which is the version of the 486 without a floating point unit. But you can see from the photo that it has a floating point unit on the die. It's unclear if Intel deliberately disabled the floating point unit to segment the market between the low-end SX and the high-end DX, or if chips with an FPU fault were sold as the SX.

A chip in a square purple ceramic package. An array of golden pins is underneath, but not visible. The package is labeled intel i486 SX.

Like 21 August at 18:35 | Open on oldbytes.space

14 comments

Ken Shirriff

One of the engineers on the 486 was Pat Gelsinger, who is now CEO of Intel. You can see his initials on the die.

A closeup of the 486 die. It has a bunch of initials in a grid, indicating people who worked on it. The initials PG are in the top center.

21 August at 18:38 | Open on oldbytes.space

Ken Shirriff

The 486 processor uses microcode. Here's a closeup of the microcode ROM; you can see the bits.

A closeup of the die showing the grid structure of the microcode ROM. Patterns of darker circles are visible.

21 August at 18:40 | Open on oldbytes.space

[DATA EXPUNGED]

Ken Shirriff

@awoodland The Pentium Pro was the first x86 processor with microcode that could be updated. Intel originally implemented that for testing purposes, but realized after the expensive Pentium FDIV bug that microcode updates were an important feature.

21 August at 19:57 | Open on oldbytes.space

Darryl Ramm

@kenshirriff I remember some beyond useless support person at Intel telling us at VMware that the Pentium did not use microcode when we were trying to find out about a bug that appeared to have a microcode fix that some but not all OEMs had released. OK well we've reversed engineered part of the update for the microcode your processors don't have, so maybe we could talk to somebody more senior?... (eventually got to senior engineering folks who were helpful)

21 August at 20:24 | Open on hachyderm.io

Ken Shirriff

Here's the 486 chip copyright, above a block of circuitry that holds the cache tags.

21 August at 18:42 | Open on oldbytes.space

Ken Shirriff

A closeup of the edge of the 486 showing bond pads with bond wires attached. Note the complex I/O driver block next to each bond pad. The pads in the center (without drivers) are two of the power and ground supplies. Note the thick vertical lines distributing power/ground to the chip.